Project Summary/Abstract The HIV-1 envelope glycoprotein gp120 plays a critical role in mediating viral entry into host cells and has been validated as a prime target for small-molecule drugs and vaccine development, yet no drugs against gp120 have been approved by the US Food and Drug Administration (FDA) to date. Therefore, there is a critical need to develop novel drugs against this target. Our group made significant headway in filling this critical need by developing a new class of HIV-1 entry inhibitors targeted to the Phe43 cavity of HIV-1 gp120. This renewal application builds on the in-depth knowledge gained during the current funding cycle from the extensive X-ray structure, synthesis, as well as the antiviral activity and toxicity data and in vitro ADMET profiles of this class of novel entry inhibitor. The development of novel therapeutics will aid in increasing the number of new and novel drugs available, especially for the treatment-experienced patients, who have limited treatment options and will extend the scope of combination therapy. This highly coordinated effort will further our goal of developing potent inhibitors for moving to the next phase of preclinical assessments in animals and for selecting two to three inhibitors as potential clinical candidates. Our long-term goal is to develop novel, highly potent, and less toxic oral anti-HIV drugs, which are expected to serve as a new arsenal for combination therapy, especially for treatment-experienced patients. We will achieve our goals by addressing four highly coordinated, hypothesis-driven specific aims: 1. Optimize next-generation HIV-1 entry antagonists by structure- based design and comprehensive medicinal chemistry. 2. Evaluate the antiviral potency, toxicity, mechanism of action, and drug resistance. 3. Measure the binding thermodynamics and determine the X-ray structure of the most potent entry inhibitors with (a) monomeric gp120 and (b) trimeric gp120. 4. Evaluate the in vitro ADMET and in vivo pharmacokinetics (PK) in laboratory animals.